1. Field of the Invention
The present invention relates to a method for correcting digital convergence, and more particularly to a digital convergence correcting method for correcting digital convergence with respect to four modes of NTSC, ED, MUSE and ZENITH only by adjusting convergence for a single mode on a software basis.
2. Description of the Prior Art
FIG. 1 is a construction view showing a conventional analog convergence correcting apparatus.
As illustrated in FIG. 1, the analog convergence correcting apparatus includes a timing controller 1 for generating a clock and a control signal required for the system by using horizontal and vertical blanking signals HBLK and VBLK synchronized with deflection as inputs, and a basic correcting waveform generator 2 for generating a waveform required for correcting convergence by using a signal from the timing controller 1. In addition to these, a first convergence corrector 3 forms a waveform required for adjusting a center and a periphery of a picture by means of a signal from the basic correcting waveform generator 2, a second convergence corrector 4 forms a waveform required for precisely adjusting the periphery of the picture by means of a signal from the basic correcting waveform generator 2, and an amplifier 5 amplifies to supply a corrected waveform from the first and second convergence correctors 3 and 4 to horizontal and vertical convergence yokes 7 through which correction current flows.
The operation of the analog convergence correcting apparatus constructed as above will be described with reference to FIGS. 2 and 3.
FIG. 2 is a crosshatch pattern for point control, and FIGS. 3A and 3B are adjustment waveforms with respect to a point six of FIG. 2.
The convergence correction is carried out by two steps of overall picture adjustment and point adjustment. The overall picture adjustment is executed in such a manner that the waveform from the basic correcting waveform generator 2 is utilized for controlling the size and polarity thereof by the first convergence corrector 3 to adjust the size, linearity, pin-cushion and key-stone with respect to overall picture. In connection with the point adjustment, the waveform from the basic correcting waveform generator 2 is utilized to be modified in the first convergence corrector 3, thereby generating various waveforms having the maximum sizes at respective points of FIG. 2 and adjusting the size and polarity of the waveforms.
For example, the basic correcting waveform as shown in FIG. 3B generated from the basic correcting waveform generator 2 is modified to have the maximum size at the point six of FIG. 2 for obtaining the waveform as shown in FIG. 3A, and the polarity and size of the obtained waveform is adjusted by an electrical variable register to allow for the point adjustment with respect to the point six of FIG. 2.
Also, the adjustment waveforms for other points of FIG. 2 can be produced by generating a waveform having the maximum size at each point.
The above-mentioned conventional analog convergence correcting system must use data corresponding to each mode by adjusting respective modes to deal with multi-mode.
Consequently, because of difficulty in processing various modes via a digital system, a conventional convergence correcting apparatus of a multi-mode projection television has been embodied in the analog system. When compared with the digital system, the analog system has drawbacks of low accuracy in adjustment, long and laborious adjustment time, unsuitable automatic adjustment in case of using a sensor, and complicated and expensive system.
FIG. 4 is a construction view showing a conventional digital convergence correcting apparatus.
As shown in FIG. 4, the digital convergence correcting apparatus includes a phase locked loop (PLL) 11 for producing a reference clock required for the system by using horizontal and vertical blanking signals HBLK and VBLK synchronized with deflection, a microcomputer 12 for calculating adjusting point data to obtain data required for the correction, and a nonvolatile EEPROM 13 for storing adjustment data of the adjusting point under the control of the microcomputer 12. Under the control of the microcomputer 12, a SRAM 15 stores correction data corresponding to the picture one by one, and a gate array 14 reads out to supply the correction data from the SRAM 15. Furthermore, a digital-to-analog (D/A) converter 16 converts digital data from the gate array 14 to an analog signal, a low-pass filter (LPF) 17 filters the correction data from the D/A converter 16, and an amplifier 18 amplifies the signals to supply a correction waveform from the LPF 17 to horizontal and vertical convergence yokes HCY and VCY.
The operation of the digital convergence correcting apparatus constructed as above will be described with reference to FIGS. 5 and 6.
FIG. 5 is a crosshatch pattern for point control, and FIG. 6 is a view for illustrating a calculating method of the correction data of FIG. 4 in the vertical direction.
The microcomputer 12 calculates the data needed for correcting convergence of a picture from the adjusting point data read out from the EEPROM 13 to store the obtained result in the SRAM 15, and the PLL 11 produces the reference clock required in the gate array 14 to read out the stored correction data by being synchronized with the horizontal and vertical blanking signals HBLK and VBLK. The gate array 14 separates the correction data read out from the SRAM 15 into each color in accordance with the reference clock from the PLL 11, and the D/A converter 16 converts to supply the separated signal into the analog signal.
The analog data from the D/A converter 16 is filtered in the LPF 17, and is amplified in the amplifier 18 for the purpose of driving the convergence yokes HCY and VCY to thereby be supplied to them.
By this operation, the convergence correction with the screen is accomplished.
In order to accomplish the adjustment in this way, there are seven adjusting points in the horizontal direction and five in the vertical direction in view of the crosshatch pattern for point control as shown in FIG. 5. Here, the inner portion of a rectangle 19 is a controlling pattern actually displayed on a screen; and that of a rectangle 20 is for describing a method for calculating the correction data from the five major adjusting points in the vertical direction, which is illustrated in FIG. 6 in detail.
Referring to FIG. 6, fourth-order polynomial interpolation obtained by five adjusting point data is written as equations 1 and 2, provided that h-numbered scanning lines exist between the adjusting points in the vertical line 20, and adjustment data of respective adjusting points are denoted by D.sub.0, D.sub.h, D.sub.2h, D.sub.3, and D.sub.4h. ##EQU1## where "s" is 4h from zero, and Li(s) is a Lagrangian coefficient which is calculated in advance using equation (2) and stored in a program area of the microcomputer to be used during the calculation.
In the above-stated calculating method according to equations (1) and (2), the value Li(s) differs for each mode during a multi-sync input, which is too bulky to be stored in the program area of the microcomputer.
Therefore, the aforesaid conventional digital convergence correcting system has a disadvantage of difficulty in embodying a multi-mode digital convergence correcting apparatus.